<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <title>Title</title>
</head>
<body>
<div id="app">
  {{ message }}
</div>
<script src="../js/vue.js"></script>
<script>
  const app = new Vue({
    el: '#app',
    data: {
      message: "你好",
    }
  })
  // 放入两个参数的问题
  const sum = (num1, num2) => {
    return num1 + num2
  }
  //  放入一个参数
  const mul = num1 => {
    return num1 * num1
  }
  // 函数代码块中有多行代码
  const test = () => {
    console.log('Hello World')
    console.log('Hello Vue')
  }
  // 函数代码块中只有一行
  const test2 = () => console.log('Hello World')  // 没有返回值 undefined
  const sum1 = (num1, num2) => num1 + num2


</script>
</body>
</html>
